This invention pertains generally to utility pliers of the type generally referred to as water pump pliers or slip-joint pliers, and more particularly pertains to utility pliers of the slip-joint type which are adapted to automatically self-adjust to the size of any work piece within the range of the jaws of the pliers by a one-hand operation.
The prior art has provided a number of different types of slip-joint pliers. Such pliers have the common characteristic of jaws offset at an angle to the plier handles and a pivot post, in the form of a bolt or rivet, mounted in the area rearward of the jaw on one of the handles and projecting through an elongated slot on the other handle. In such pliers, means for enabling selective spacing of the distance between the jaws is variously provided by spaced-apart ridges or teeth along the inside long edge of the slot adapted for selective binding engagement with the pivot post. Another well-known method of providing distance adjustment between the jaws in such pliers is the provision of spaced-apart arcuate ridges on the interfacing surfaces adjacent the pivot point. All such tools, to be adjusted to the size of a particular work piece to be gripped between the jaws, require a two-handed operation wherein the handles are pulled wide apart to permit a sliding action of the pivot post along the slot to move the jaws to the desired work piece size.
Self-adjusting utility pliers are disclosed in U.S. Pat. No. 4,651,598; issued Mar. 24, 1987. The tool therein disclosed is intended for the same use and purpose as the aforedescribed prior art pliers but has the clear advantage of single-handed adjustment. Further, the pliers are adapted to slideably close upon a work piece in response to manual closing action on the handles, and, in response to contact with the work piece, automatically lock against further sliding action and shift from the sliding to a pivoting mode whereby continued exertion of manual force on the handles causes increased gripping action on the work piece.
The typical prior art slip-joint pliers which require two-handed adjustment, as heretofore described, are usually mass-produced by a drop forging operation, the handle members are solid metal, and the area of connection between the two handle members is relatively planar and thin, whereas the gripping jaws are laterally inwardly widened to provide gripping surfaces which overlap into the plane of the center point of the axis of the pliers' interconnecting pivot. The aforementioned self-adjusting utility pliers also are most easily adaptable to a substantially solid handle member construction obtainable through a forging operation.